Devices to actuate downhole tools such as external casing packers, for example normally require an inner string to shift a sliding sleeve or a straddle tool to bridge over an inflate port to set the downhole tool. Other techniques involve dropping a ball on a seat or pressurizing the wellbore. Each of these techniques for setting a downhole tool has limitations in certain well conditions and associated costs to implement.
What is needed and made possible by the present invention is a technique to set a downhole tool in an alternative way based on conditions that exist in the wellbore. In a specific embodiment exposure to well fluids at a predetermined temperature for a predetermined time allows the tool to be set. These and other advantages of the present invention will be more apparent to those skilled in the art from a review of the description of the preferred embodiment and associated drawings and the claims that all appear below.